Materials handling consultancy LSL Consulting expects to complete commissioning of the major parts of its portion of the Grootegeluk Medupi Expansion Project (GMEP) and the discards backfill project at the Limpopo-based Grootegeluk coal mine, which is owned and operated by coal and heavy minerals mining company Exxaro Resources, this month.

“Having been involved in the GMEP project from prefeasibility to final handover for the last seven years, key project highlights for LSL include the introduction of semi-mobile in-pit crushing plants complete with an in-pit conveyor system, which will be relocated and extended as mining progresses,” LSL project manager Jan Gerber says.

He notes that, not only is this a shift from the fixed outside crushing plants, but it also reduced the need for haul truck operations, adding that in-pit crushing and conveying will simplify materials handling processes and save on mine operating costs.

LSL engineering manager Manie Krause agrees, suggesting that the in-pit crushing system at GMEP, is “one of the biggest in the country”, capacity-wise. The system was designed as a dual system with the GG8 system designed for run-of-mine (RoM) coal capacity of 6 000 t/h for beneficiation, and the GG7 system for RoM coal at 3 000 t/h for feed directly to the product blending beds.

Gerber explains that the semi-mobile in-pit crushing systems will be moved on a mobile crawler system, designed to carry 500 t, when required.

“As a result, the mine operators can move the crushing plant to remain close to the mining face, thereby reducing materials hauling distances,” he says, further noting that, over the life-of-mine, the systems could be relocated over a distance of 4 km.

This same crawler system will also be used for the relocation of the 300 t discards backfill shiftable conveyor drive station and for supporting the discards spreader bridge during shifting of the backfill system.

Having been involved in the engineering of the discards backfill project for the past four years, Gerber highlights the unique features and challenges of this project, which involved the detailed design and construction of the conveyors and drive stations, including the design and construction of permanent structures on backfilled material.

“With the backfilled material continuously settling, it creates a distinctive challenge. LSL had to take future vertical backfill material movement and future settlements into account,” he tells Mining Weekly, pointing out that the backfill material will continue to settle for at least the next twenty years, albeit at a continuously reducing rate of settlement.

Backfilling plant discards material will be placed using a crawl-mounted spreader, a 2-km-long shiftable conveyor and a series of extendable conveyors on two 35-m-deep benches for upper and lower systems. Each bench will be continuously sealed with overburden to prevent spontaneous combustion of the stacked discards, based on requirements established by Exxaro during extensive testing and research, Gerber explains.

He highlights that one of the achievements of the discards backfill project is the use of two tight curved overland conveyors, implemented as a result of space constraints, to transport the discard material from a 50 000 t bunker towards the pit. Another highlight is the extendable and shiftable conveyors, which have mobile drive stations comprising 1.5 MW and 2 MW drives respectively. Each mobile drive station is complete with modular conveyor components, cable reels, conveyor drives and take-up systems, as required.

“The mobile drive stations substantially reduce the time required for moving, as few electrical disconnections and reconnections are required,” Gerber adds.

The backfill project also involves a decline conveyor system that regenerates about 460 kW of power into the electricity grid during operation, Krause says. This required a sophisticated brake system for the conveyor to ensure controlled stopping and starting under load. He notes that regenerative variable speed drive (VSD) systems have mostly been implemented at sugar mills in South Africa to date, and the Grootegeluk installation is “probably a first for regenerative conveyor systems in South Africa”.

LSL MD Dimitri Simigiannis adds that LSL designed the new Grootegeluk materials handling plant to be maintenance friendly, ensuring efficient maintenance when required, as well as energy efficient, according to the specifications and goals of the energy efficiency commission. Exxaro awarded the Exxaro and LSL project team an Evergreen Award for innovative design of the GMEP coal dispatch system, which allows feed from any one of the existing Matimba or the new Medupi product blending beds to either the Medupi or Matimba power stations.

He notes that the introduction of retractable return idlers and VSDs on most of the conveyor systems are some of the latest technologies used at the project to enable high-quality product delivery.

Simigiannis further mentions that Grootegeluk has the world’s largest beneficiation complex where 8 000 t/h of RoM coal is beneficiated in six different plants. The new dense media separation facilities, the Grootegeluk 7 and Grootegeluk 8 beneficiation plants, handle the coal beneficiation process.

Although the GMEP in-pit materials handling plant, as well as the discards backfill project, reached their project peaks simultaneously, creating some strain for construction and other resources, Simigiannis emphasises the significance of the achievement of a project of this magnitude in the current economic climate, adding that GMEP is “possibly the largest project LSL has embarked on”.

“Since LSL Consulting has been involved in Grootegeluk for the past 30 years, we have a long-standing relationship with Exxaro and a good understanding of the mine,” he stresses, concluding that the company will continue with expansion studies for the mine.